Named for energy firm BP, which
donated $5 million toward its construction, it
is the first Gehry-designed bridge to have been completed.[5] BP
Bridge is described as snakelike because of its curving form.[6]
Designed to bear a heavy load without structural problems caused by
its own weight, it has won awards for its use of sheet metal. The bridge
is known for its aesthetics, and Gehry's style is seen in its
biomorphic allusions
and extensive sculptural use of stainless steel plates to express
abstraction.

The pedestrian bridge
serves as a noise
barrier for traffic sounds from Columbus Drive. It is a
connecting link between Millennium Park and destinations to the
east, such as the nearby lakefront, other parts of Grant Park and a
parking garage.[7] BP
Bridge uses a concealed box girder design with a concrete base, and
its deck is covered by hardwood floor boards.[8]
It is designed without handrails, using stainless steel parapets instead. The total
length is 935 feet (285 m), with a five percent slope on its
inclined surfaces that makes it barrier free and
accessible to all. Although the bridge closes in winter because ice
cannot be safely removed from its wooden walkway, it has received
favorable reviews for its design and aesthetics.

Contents

Design

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Preliminary
plans

Since the mid 19th century, Grant Park has been Chicago's front
yard, with Lake
Michigan to the east and the Loop to the west. Columbus Drive runs
north–south through Grant Park, with Daley Bicentennial Plaza in
the northeast corner of the park. West of Columbus Drive, the
northwest corner of the park had been Illinois Central rail yards
and parking lots until 1997, when it became available for
development by the city as Millennium Park. Millennium Park is also
north of Monroe Street and the Art Institute, east of Michigan Avenue, and south of
Randolph Street.[9]
For the year 2007, Millennium Park trailed only Navy Pier as a Chicago
tourist attraction.[10]

In February 1999, the city announced it was negotiating with
Frank Gehry to design a proscenium arch and orchestra enclosure for
a band
shell in the new park, as well as a pedestrian bridge crossing Columbus Drive
between Millennium Park and Daley Bicentennial Plaza. The city also
sought donors to cover the cost of Gehry's work, which would
eventually become Jay Pritzker Pavilion and the BP Pedestrian
Bridge.[11][12] At
the time, the Chicago Tribune dubbed Gehry "the
hottest architect in the universe" in reference to the acclaim for
his Guggenheim Museum Bilbao.[13]
Millennium Park project manager Edward Uhlir said "Frank is just
the cutting edge of the next century of architecture", and noted
that no other architect was being sought.[11]
Gehry was approached several times by Skidmore, Owings, & Merrill architect
Adrian Smith on behalf of the
city.[3]
In April 1999, the city announced that the Pritzker family had
donated $15 million to fund Gehry's band shell and an
additional nine donors committed a total of $10 million more
to the park.[2][14] That
same day, Gehry agreed to the design request.[4]

In November 1999, when he unveiled his initial plans for the
bridge and band shell, Gehry admitted the bridge's design was
underdeveloped because funding for it was not yet committed. Even
at this early point, the need for a sound barrier for Columbus
Drive traffic noise was recognized, although Gehry indicated this
might take the form of a berm, or
raised barrier.[15] The
need to fund a bridge to span the eight-lane Columbus Drive was
evident, but some planning for the park was delayed in anticipation
of details on the redesign of Soldier Field.[16] In
January 2000, the city announced plans to expand the park to
include features that became Cloud Gate, Crown
Fountain, the McDonalds Cycle
Center, and the BP Pedestrian Bridge.[17] Later
that month, Gehry unveiled his next design, which depicted a
winding bridge.[18]

While the neighboring Jay Pritzker Pavilion changed relatively
little from Gehry's 1999 design when built, the bridge went through
several proposed designs.[19]
The proposal made in early 2000, which was expected to be executed
in 2002, included a bridge that was a mere 170 feet
(51.8 m) long and 20 feet (6.1 m) wide.[20]
That design was not approved, and Chicago MayorRichard M.
Daley's disapproval of Gehry's subsequent design of an
800–900-foot (240–270 m) bridge caused Gehry to come up with
ten more designs.[21]
The first of these plans was for a Z-shaped bridge that would have
run northwest–southeast with western ramps in Millennium Park,
leading south, and eastern ramps in the empty north section of
Daley Bicentennial Plaza, leading north. It would have required
elevators to conform to the Americans with Disabilities Act.[19]
This plan was abandoned because it would have segregated the
handicapped.[22] Gehry
had only designed two bridges previously, both in the mid-1990s
(Pferdeturm USTRA Bridge in
Hanover, Germany and Financial Times Millennium Bridge
in London, United Kingdom) but neither was
built.[19]

Final
plan

The final design for the bridge was revealed in an exhibit at
the Chicago Cultural Center on June
10, 2000.[21]
As designed and built, the bridge is 935 feet (285.0 m)
long and 20 feet (6.1 m) wide, with a 14-foot-6-inch
(4.42 m) Columbus Drive clearance.[23][24] The
clearance was designed to slightly exceed the 14-foot (4.3 m)
standard set by the United States
Department of TransportationFederal Highway
Administration for urban area interstate bridge clearances, and
to allow for additional future layers of pavement below.[25] This
height is also greater than the maximum vehicle height of
13 feet 6 inches (4.1 m) set by the Illinois Vehicle
Code.[26]
According to the Chicago Tribune the width of the
"trenchlike" area spanned is approximately 150 feet
(46 m),[21]
while The New York Times reports the
bridge is over ten times longer than Columbus Drive is wide.[27]

BP Bridge begins in Millennium Park between the trellis system over the Jay Pritzker
Pavilion's great lawn and the Lurie Garden; the design was changed so
that the west ramp coincided with the boardwalk of the Lurie Garden
seam.[28][29] The
bridge winds its way northward along the eastern edge of Millennium
Park before crossing Columbus Drive in a C-shaped curve, above
underground parking garage entrances. In Daley
Bicentennial Plaza the bridge has an S-shape, then turns east. BP
Bridge is designed so that its inclined surfaces have a continuous
five percent slope rather than landings and switchback
ramps, which provides easy access for the physically
challenged.[21][30] The
gently sloped ramp eliminates the need for lifts or any of the
other common types of ramps (L-shaped, switchback, U-shaped,
straight),[31] and
helped the park earn the 2005 Barrier-Free America Award for its
exemplary barrier-free design.[32]

Gehry had hoped to design the bridge so that it could be
constructed without a support column in the center of Columbus
Drive. However, Chicago Tribune architecture
critic Blair Kamin
notes that if he had done so, the bridge might not have been as
sleek.[6]
Building the bridge without the column would have required
load-bearing cantilevers (beams supported only on one side) from
structural positions on opposite sides of the street; this would
have been expensive and labor-intensive, because it would have
required excavating large portions of the parking garages on both
sides of the street. Moreover, on the Daley Bicentennial Plaza
side, the optimal location for the supporting cantilever would have
been at the location of the Monroe Street Garage. Thus, the
preferred bridge design was altered to avoid problems related to
the underground parking garages.[33]

The bridge is both a connector and a viewing platform for the
park.[6]
It was designed to link the Historic Michigan Boulevard District
and the entire Loop to the west with the Lake Michigan lakefront to
the east. It was also designed to be a berm noise barrier
blocking noise on the eight-lane Columbus Drive from the Park's
outdoor band shell (Jay Pritzker Pavilion), by deflecting traffic
sounds upward.[34]

The bridge, which uses steel girders, reinforced concrete abutments and deck slabs, hardwood deck, and a
stainless steel veneer, cost between $12.1 and
$14.5 million.[34][35][36] It
contains large sculptural plates of curvilinear stainless
steel instead of more standard flat plates.[1]
The bridge's curvilinear design gives it a flowing, natural look,
instead of the linear, rigid form of standard bridges. Although its
steel girders rest on concrete pylons and most of the bridge is solid concrete,
the bridge uses a hollow box girder design to minimize weight, as the
ground that supports the bridge covers underground parking
garages.[8][37]
The concrete base and box girder are flanked by a hollow stainless
steel skeleton.[8]
Despite its hollow structure, and the fact that it is designed as a
concealed beam
bridge, the footbridge is built to highway standards and
can support a full capacity load of pedestrians.[37]
The bridge is designed without standard handrails and uses waist-high parapets as guard rails instead.[6]

Construction

BP Bridge entry and redesigned landscape in Daley Bicentennial
Plaza

The bridge was built using 22-gauge stainless
steel type
316 plates (0.031 inches/0.79 millimetres thick), with an
angel hair
finish and a flat interlocking panel process. Stainless steel
type 316 is known for its excellent welding characteristics, as well as for its
resistance to pitting.[38]
According to the Chicago Tribune, the bridge materials
used in construction include 2,000 rot-resistant Brazilian hardwood boards for the deck, 115,000
stainless steel screws and 9,800
stainless
steelshingle
plates.[28][37]
According to Architecture Metal Expertise, the bridge has "10,400
stainless steel trapezoidal panels in 17 different shop fabricated
configurations [which] involved 1,000 shop hours".[34]
The sheet metal work totaled 5,900 field hours over a
six-month period.[34]
During construction, about 200 shingles were installed per
day.[39] The
bridge includes two types of structural steel: steel that is
2.0 inches/5.1 centimetres thick and 20.0 inches/51
centimetres in diameter for the approaches and box girders for the
span.[40]

CATIA software was used to
handle the complex geometric layout.[41]
To ensure accurate fitting and alignment to the sloping, curving
sides of the bridge, 4,400 custom-made convex, concave and radiused
cladding panels were fabricated on site by sheet metal contractor
Custom Metal Fabricators (CMF). CMF used 57,000 square feet
(5,300 m2) of stainless steel sheet to cover the
sides, which have a combined perimeter length of 1,728 feet
(526.7 m). CMF built special heated enclosures so that work
could continue on site through the winter. They designed,
fabricated and installed custom type 4 brushed stainless steel
parapets serving in the place of handrails on the bridge. CMF
earned the 2005 Tom Guilfoy Memorial Architectural Sheet Metal
Award, by the California chapter of the
Sheet Metal and Air Conditioning Contractors' National
Association for the project.[34]
In 2005 it received a Merit Award from the National Steel Bridge
Alliance, and an Excellence in Structural Engineering award
from the Structural Engineers Association of
Illinois.[42]

On the day that the two halves of the bridge were joined, each
side of Columbus Drive was closed for a 12-hour period and a 360-short-ton (320-long-ton; 330 t) crane was used to install the girders.
Before bringing the jack to the location, screw jacks were used to
shore up the underground garage roof to hold the crane's
weight.[43]

The landscaping surrounding the bridge was redesigned by landscape
architect Terry Guen. Honey locusts, ash and maple
trees were removed and replaced with three varieties of magnolia and more than two
dozen ornamental and canopy trees along
the eastern foot of the bridge in Daley Bicentennial Plaza. Other
preliminary construction work included setting reinforcing rods for
the bridge in the concrete roof deck of the parking garage located
under the park.[23]

Use and
controversies

The deck is covered with 2,000 Brazilian hardwood floor
boards.

Before its official opening, the bridge had a May 22, 2004
private ribbon-cutting ceremony attended by Gehry and Mayor Daley.
During the weekend of the ribbon-cutting, Gehry was awarded an honorary degree
from the School of the Art
Institute of Chicago.[44]
The BP Pedestrian Bridge officially opened, along with the rest of
Millennium Park, on July 16, 2004.[1][37]
It remained unnamed at the ribbon-cutting,[37]
but before the July park opening, energy firm BP had paid $5
million for the bridge sponsorship and naming rights.[45]

Timothy Gilfoyle, author of Millennium Park: Creating a
Chicago Landmark, notes that a controversy surrounds the
"tasteless" corporate naming of several of the Park's features,
including the bridge, which was named after an oil company.[46] It is
well-documented that naming rights were sold for high fees,[47] and
Gilfoyle was not the only one who chastised park officials for
selling naming rights to the highest bidder. Public interest groups
have crusaded against commercialization of Chicago parks.[48]
However, many of the donors have a long history of local
philanthropy and the funds were essential to providing necessary
financing for several features of the park.[45]

After the park opened, some of the bridge's foibles became
apparent. The bridge has had to be closed during the winter because
freezing conditions make it unsafe.[49] Since
the bridge is over an expressway-like trench of Columbus Drive,
shovelling the snow onto passing cars is not an option and the
Brazilian hardwood would be damaged by rock salt.[50] The
city not only mandates that the bridge be swept and washed daily,
but also that the parapets be wiped free of fingerprints.[51]

The bridge has also had controversial closures in the summer,
which were related to larger park concerns. On September 8, 2005,
Toyota Motor Sales USA paid $800,000 to
rent the bridge and all but four venues in the park from
6 a.m. to 11 p.m.[52][53]
On August 7, 2006, Allstate paid $700,000 to rent the bridge and
most of the park for a day.[54][55]
Excluding commuters who normally walk through the park and tourists
lured by its attractions was controversial, though the city said
the money raised paid for free public programs in Millennium
Park.[52]

Aesthetics

The bridge is noted for its sculptural characteristics and Kamin
describes it as a delightful pleasure that was designed to
emphasize its artistic elements while de-emphasizing its concrete
and steel support system.[6]The New York Times notes that the artist Anish Kapoor's
attempts to hide Cloud
Gate's seams were an interesting contrast to Gehry's
architectural efforts. Gehry took pride in making the BP Pedestrian
Bridge flaunt its seams.[27]

Beginning with Gehry's earliest bridge designs, the bridge was
expected to complement the neighboring Pritzker Pavilion.[20]
Some have suggested that the bridge and the pavilion are mere
extensions of Gehry's work in other cities. For example, according
to Gilfoyle, both structures embody Gehry's established
asymmetrical style, evoking fluid, continuous motion and sculptural
abstraction. They also feature metallic facades and aesthetic
curves, but they are said to be more refined, reduced and dynamic
than much of his other work.[57]

Since the 1960s, Gehry has made artistic use of scaled animals
such as fish and snakes, which first appeared in his architectural
designs in the 1980s.[58][59][60] Many
references to the bridge describe it as snakelike for its winding path,[6][34][44]
and some even refer to the stainless steel plates as scales with
discussion of reptilian
forms.[19][41]
Kamin calls it "a bridge that resembles a giant silver snake,
complete with a scaly skin",[6]
while Gehry said he thought the bridge looked like a river, but
added he might be the only one who thought that.[44]

The way the bridge flows in a continuum of unexpected directions
is a break from Gehry's other work and other more traditional urban
and architectural forms nearby.[57]Pulitzer
Prize-winning architecture critic Kamin gave the bridge four
stars (out of a possible four) in his review and admires how
"computers have given Gehry unparalleled formal freedom" to design
"the complexity of its geometry" and multidimensional
curvatures.[6]
The bridge provides views of both the Historic Michigan Boulevard
District and Lake Michigan in a way that Kamin says makes it a belvedere.[6][61] Kamin
also recommends anyone having a bad day stroll across the bridge,
adding "You won't get where you're going quickly, but you'll feel a
whole lot better once you're done."[6]

^
The four venures in Millennium Park that were not rented by Toyota
were Wrigley
Square, Lurie Garden, the McDonald's Cycle Center and Crown
Fountain. Allstate acquired the visitation rights to Pritzker
Pavilion, BP Bridge, Lurie Garden and the Chase Promenades, and only had exclusive
access to Cloud Gate after 4 p.m.

^
As of 2009, the recently constructed Legacy Tower blocks the view of the bridge
and Millennium Park from Sears Tower at least partially.